feat: rootParams

packages/next/server.d.ts

@@ -14,6 +14,7 @@ export { URLPattern } from 'next/dist/compiled/@edge-runtime/primitives/url'
 export { ImageResponse } from 'next/dist/server/web/spec-extension/image-response'
 export type { ImageResponseOptions } from 'next/dist/compiled/@vercel/og/types'
 export { unstable_after } from 'next/dist/server/after'
+export { unstable_rootParams } from 'next/dist/server/request/root-params'
 export { connection } from 'next/dist/server/request/connection'
 export type { UnsafeUnwrappedSearchParams } from 'next/dist/server/request/search-params'
 export type { UnsafeUnwrappedParams } from 'next/dist/server/request/params'

packages/next/server.js

@@ -13,6 +13,7 @@ const serverExports = {
     .URLPattern,
   unstable_after: require('next/dist/server/after').unstable_after,
   connection: require('next/dist/server/request/connection').connection,
+  unstable_rootParams: require('next/dist/server/request/root-params'),
 }
 
 // https://nodejs.org/api/esm.html#commonjs-namespaces
@@ -28,3 +29,4 @@ exports.userAgent = serverExports.userAgent
 exports.URLPattern = serverExports.URLPattern
 exports.unstable_after = serverExports.unstable_after
 exports.connection = serverExports.connection
+exports.unstable_rootParams = serverExports.unstable_rootParams

packages/next/src/build/webpack/plugins/next-types-plugin/index.ts

@@ -283,6 +283,7 @@ function formatRouteToRouteType(route: string) {
 
 // Whether redirects and rewrites have been converted into routeTypes or not.
 let redirectsRewritesTypesProcessed = false
+let collectedRootParams: Map<string, string[]> = new Map()
 
 // Convert redirects and rewrites into routeTypes.
 function addRedirectsRewritesRouteTypes(
@@ -584,6 +585,63 @@ function formatTimespanWithSeconds(seconds: undefined | number): string {
   return text + ' (' + descriptive + ')'
 }
 
+function getRootParamsFromLayouts(layoutsMap: Map<string, string[]>) {
+  let shortestLayoutLength = Infinity
+  const rootLayouts: { route: string; params: string[] }[] = []
+  const allRootParams = new Set<string>()
+
+  for (const [route, params] of layoutsMap.entries()) {
+    const segments = route.split('/')
+    if (segments.length <= shortestLayoutLength) {
+      if (segments.length < shortestLayoutLength) {
+        rootLayouts.length = 0 // Clear previous layouts if we found a shorter one
+        shortestLayoutLength = segments.length
+      }
+      rootLayouts.push({ route, params })
+      params.forEach((param) => allRootParams.add(param))
+    }
+  }
+
+  const result = Array.from(allRootParams).map((param) => ({
+    param,
+    // if we detected multiple root layouts and not all of them have the param,
+    // then it needs to be marked optional in the type.
+    optional: !rootLayouts.every((layout) => layout.params.includes(param)),
+  }))
+
+  return result
+}
+
+function createServerDefinitions(
+  rootParams: { param: string; optional: boolean }[]
+) {
+  return `
+  declare module 'next/server' {
+
+    import type { AsyncLocalStorage as NodeAsyncLocalStorage } from 'async_hooks'
+    declare global {
+      var AsyncLocalStorage: typeof NodeAsyncLocalStorage
+    }
+    export { NextFetchEvent } from 'next/dist/server/web/spec-extension/fetch-event'
+    export { NextRequest } from 'next/dist/server/web/spec-extension/request'
+    export { NextResponse } from 'next/dist/server/web/spec-extension/response'
+    export { NextMiddleware, MiddlewareConfig } from 'next/dist/server/web/types'
+    export { userAgentFromString } from 'next/dist/server/web/spec-extension/user-agent'
+    export { userAgent } from 'next/dist/server/web/spec-extension/user-agent'
+    export { URLPattern } from 'next/dist/compiled/@edge-runtime/primitives/url'
+    export { ImageResponse } from 'next/dist/server/web/spec-extension/image-response'
+    export type { ImageResponseOptions } from 'next/dist/compiled/@vercel/og/types'
+    export { unstable_after } from 'next/dist/server/after'
+    export { connection } from 'next/dist/server/request/connection'
+    export type { UnsafeUnwrappedSearchParams } from 'next/dist/server/request/search-params'
+    export type { UnsafeUnwrappedParams } from 'next/dist/server/request/params'
+    export function unstable_rootParams(): Promise<{ ${rootParams
+      .map(({ param, optional }) => `${param}${optional ? '?' : ''}: string`)
+      .join(', ')} }>
+  }
+  `
+}
+
 function createCustomCacheLifeDefinitions(cacheLife: {
   [profile: string]: CacheLife
 }) {
@@ -855,6 +913,22 @@ export class NextTypesPlugin {
       if (!IS_IMPORTABLE) return
 
       if (IS_LAYOUT) {
+        const rootLayoutPath = normalizeAppPath(
+          ensureLeadingSlash(
+            getPageFromPath(
+              path.relative(this.appDir, mod.resource),
+              this.pageExtensions
+            )
+          )
+        )
+
+        const foundParams = Array.from(
+          rootLayoutPath.matchAll(/\[(.*?)\]/g),
+          (match) => match[1]
+        )
+
+        collectedRootParams.set(rootLayoutPath, foundParams)
+
         const slots = await collectNamedSlots(mod.resource)
         assets[assetPath] = new sources.RawSource(
           createTypeGuardFile(mod.resource, relativeImportPath, {
@@ -933,6 +1007,20 @@ export class NextTypesPlugin {
 
           await Promise.all(promises)
 
+          const rootParams = getRootParamsFromLayouts(collectedRootParams)
+          // If we discovered rootParams, we'll override the `next/server` types
+          // since we're able to determine the root params at build time.
+          if (rootParams.length > 0) {
+            const serverTypesPath = path.join(
+              assetDirRelative,
+              'types/server.d.ts'
+            )
+
+            assets[serverTypesPath] = new sources.RawSource(
+              createServerDefinitions(rootParams)
+            ) as unknown as webpack.sources.RawSource
+          }
+
           // Support `"moduleResolution": "Node16" | "NodeNext"` with `"type": "module"`
 
           const packageJsonAssetPath = path.join(

packages/next/src/server/app-render/create-component-tree.tsx

@@ -331,6 +331,10 @@ async function createComponentTreeInternal({
   // Resolve the segment param
   const actualSegment = segmentParam ? segmentParam.treeSegment : segment
 
+  if (rootLayoutAtThisLevel) {
+    workStore.rootParams = currentParams
+  }
+
   //
   // TODO: Combine this `map` traversal with the loop below that turns the array
   // into an object.

packages/next/src/server/app-render/work-async-storage.external.ts

@@ -7,6 +7,7 @@ import type { DeepReadonly } from '../../shared/lib/deep-readonly'
 import type { AppSegmentConfig } from '../../build/segment-config/app/app-segment-config'
 import type { AfterContext } from '../after/after-context'
 import type { CacheLife } from '../use-cache/cache-life'
+import type { Params } from '../request/params'
 
 // Share the instance module in the next-shared layer
 import { workAsyncStorage } from './work-async-storage-instance' with { 'turbopack-transition': 'next-shared' }
@@ -69,6 +70,8 @@ export interface WorkStore {
     Record<string, { files: string[] }>
   >
   readonly assetPrefix?: string
+
+  rootParams: Params
 }
 
 export type WorkAsyncStorage = AsyncLocalStorage<WorkStore>

packages/next/src/server/async-storage/work-store.ts

@@ -112,6 +112,8 @@ export function createWorkStore({
 
     isDraftMode: renderOpts.isDraftMode,
 
+    rootParams: {},
+
     requestEndedState,
     isPrefetchRequest,
     buildId: renderOpts.buildId,

packages/next/src/server/lib/patch-fetch.ts

@@ -669,7 +669,7 @@ export function createPatchedFetcher(
                 )
                 await handleUnlock()
 
-                // We we return a new Response to the caller.
+                // We return a new Response to the caller.
                 return new Response(bodyBuffer, {
                   headers: res.headers,
                   status: res.status,

packages/next/src/server/request/draft-mode.ts

@@ -176,7 +176,7 @@ class DraftMode {
     return false
   }
   public enable() {
-    // We we have a store we want to track dynamic data access to ensure we
+    // We have a store we want to track dynamic data access to ensure we
     // don't statically generate routes that manipulate draft mode.
     trackDynamicDraftMode('draftMode().enable()')
     if (this._provider !== null) {
@@ -229,7 +229,7 @@ function trackDynamicDraftMode(expression: string) {
   const store = workAsyncStorage.getStore()
   const workUnitStore = workUnitAsyncStorage.getStore()
   if (store) {
-    // We we have a store we want to track dynamic data access to ensure we
+    // We have a store we want to track dynamic data access to ensure we
     // don't statically generate routes that manipulate draft mode.
     if (workUnitStore) {
       if (workUnitStore.type === 'cache') {